Method for purification of aluminum



March 12, 1968 J. MERLES METHOD FOR PU RIFICATION OF ALUMINUM 2Sheets-Sheet 1 Filed July 14, 1964 FIG. 1

I N V E N TOR Jacques Merlas March 12, 1968 J. MERLES METHOD FORPURIFICATION OF ALUMINUM Filed July 14, 1964 2 Sheets-Sheet 2 NV E NTORFIGJL United States Patent 27 Claims. for. 75-43 This invention relatesto the purification of aluminum and more particularly to the method andmeans for the purification of aluminum by liquid mercury.

In United States Patent No. 2,198,673, description is made or"purification of aluminum, such as impure aluminum in a finely dividedstate, by solution of the impure aluminum in hot liquid mercury todissolve aluminum and leave the impurities in an undissolved state forsubsequent separation by decantation and then distillation of thesolution to separate the mercury from the dissolved aluminum. Thedescribed procedures are well carried out in an inert atmosphere atsubatmospheric pressure.

In Fiat, Review of German Sciences, Metallkunde 39- 45, Borschers andSchmidt Process, description is made of the separation of aluminum fromits solution in mercury by first cooling to precipitate aluminumenriched crystals and thereafter performing a preliminary mechanicalrefining step and then effecting complete removal of the mercury, as bydistillation.

In Beliaiev, Firsanova and Rapoporte, Electro-metallurgy of Aluminum,Moscow 1953, pp. 675-684, description is made of the extraction ofaluminum from the pasty mass of aluminum amalgam obtained bycrystallization by means of a screw conveyor or by compression in ahydraulic press.

The procedures described in the aforementioned articles and also inGerman Patent No. 846,796 depend upon solution of the aluminum inmercury in an autoclave maintained at a pressure of to atmospheres and atemperature within the range of 500 to 650 C. to maximize the solutionof aluminum.

The described processes of extraction, which operate under highpressure, are subject to a number of technological dilficulties. Thesteel of which such equipment is formed must be capable of withstandinghigh temperatures and pressures as well as the corrosive action of thealuminum amalgam. The thicknesses of the steel walls militate againstthe desirable rate of heat exchange. The conditions of pressure,temperature and liquid levels call for complex and delicate controls.Aside from the foregoing, a principal difficulty resides in theinability to achieve sufiicient tightness in the equipment to resist theescape of poisonous vapors of mercury, especially when operating underthe positive pressure conditions with the equipment and especiallybetween the joints, as in the areas of extension of rotating shaftsthrough the walls of the equipment. Difficulties arise also inmaintenance of fluid and vapor tightness at the inlets and the outletsused for the introduction or removal of material in the system.

Dilficulty is also experienced in the maintenance of high temperaturesand pressures in uniform distribution for optimum solution of thealuminum and separation of impurities. The presence of hot spots hasbeen found to cause vaporization while the presence of cold spots leadsto condensations thereby to interfere with the elficiency of operationof the equipment and control of the process.

Aluminum in the form of chips, shavings or other divided particles ofimpure aluminum dissolves so slowly inmercury at near boiling pointtemperature and atmospheric pressure as to make the described processcornmercially impractical.

assignor to Chimiques et Elec- Various pretreatments have been appliedin the effort to make impure aluminum more readily soluble in mercurysuch as in the pre-engagement of the mercury with an alloy of aluminum,as described in German Patent No. 840,765, or treatment of the impurealuminum with metal salts or other reagents which react with aluminumoxide at temperatures of about 360 C., as described in Fiat, supra, butthese have not been efiective to overcome the deficiencies as previouslypointed out.

It is an object of this invention to provide a method and means for thepurification of aluminum by the use of liquid mercury to separateimpurities from the aluminum and it is a related object to provide amethod and means of the type described which is free of any of thedeficiencies of the processes previously described.

An object of this invention is to provide a process and means for theproduction of purified aluminum by solution of the impure aluminum inhot mercury, preferably in the absence of air, elimination ofundissolved impurities, cooling to precipitate crystals of aluminumamalgam, and vaporizing off the mercury from the separated ama1- gam toleave purified aluminum, and it is a related object to carry out thesteps of solution, elimination of impurities, crystallization andseparation of the amalgam to free aluminum in a continuous operation.

A further object is to effect dissolution of aluminum from the impurealuminum by trickling liquid mercury over the impure aluminum at atemperature within the range of 300 to 420 C., and preferably at atemperature within the range of 340 to 380 C., wherein the impurealuminum is treated while in a solid state, such as in the form ofsheets, wires, turnings, chips, granules and waste from the conventionaltreatments used with alloy and alloys of aluminum or semi-finishedproducts and the like, which materials may or may not have beensubjected to pretreatment, with the impure aluminum preferably beingmaintained in a stationary bed relative to the dissolving mercury. l

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, and embodiment of the invention is shown in the accompanyingdrawings, in which- FIG. 1 is a diagrammatic view of a completeinstallation embodying the practice of this invention;

FIG. 2 is a schematic sectional elevational view of a portion of theinstallation of FIG. 1 illustrating. means for the solution of aluminumin mercury in accordance with the practice of this invention;

FIG. 3 is a schematic view of the arrangement ofelements for heating themercury and for introducing the heated mercury into the process circuit;and

FIG. 4 is a schematic elevational view of the arrangement of elementsfor the removal of mercury by distillation.

Referring now to the drawings, in FIG. 1, the numeral 1 represents thegrid on which the impure aluminum to be dissolved is adapted to rest, 2represents the orifices through which the mercury jets serving assolvent escape, 3 is the mercury pump of the dissolving installation, 4is the mercury-collecting tank at the base of the dissolving column, 5is the overflow of this tank, 6 is the circuit of liquid mercury servingas solvent, 7 is the part of this circuit in which the heating of thismercury is carried out for dissolving purposes, 8 is the opening of thiscircuit into the dissolvng column, 9 is the feed chamber for theintermittent introduction of the impure aluminum, 10 and 11 are theinlet and outlet valves of the feed chamber, 12 and 13 represent theinlet and outlet for the nitrogen or other inert gas serving to flushout the air of the feed chamber, and 14 is the circuit of mercurysaturating vapor intended for the heating of the installation. 30 is theextraction screw mounted for rotational movement in the tubular housingfor the impurities, 31 is the receiver which communicates with theopening 31 in the upper end portion of the screw housing 30 throughwhich the impurities fall for recovering the impurities, 32 and 33 arethe upper and lower valves of this receiver, 34 and 35 represent theinlet and the outlet of the flushing nitrogen or other inert gas forflushing air from the receiver, 39 is the plumbago or graphite cruciblein which the impurities are collected, 36 is the overflow for the flowof the aluminum amalgam solution freed from impurities, 37 are viewingarrangements for observation of the interior of the screw conveyor, and38 is a conduit communicating with a nitrogen atmosphere. 40 is theextraction screw for the amalgam crystallized by cooling, 47 is thedouble water-cooling jacket for the purified solution, 41 is the lockchamber for receiving the crystallized aluminum amalgam, 42. and 43 arethe upper and lower inlet and outlet valves of this chamber, 44 and 45are the inlet and the outlet for the flushing nitrogen or other inertgas for flushing air from the chamber, and 46 is the graphite cruciblein which the crystallized amalgam is collected.

In FIG. 2, 15 indicates the height of the column of impure aluminumsprinkled with the mercury jets serving as solvent, 16 represents theheight of the column of the impure aluminum 25 in the chamber, 17 is themercury hydraulic joint for the shaft 1", interconnecting the pump 3with the drive motor 18, While 23 and 24 are flow meters. The doublejacket of the dissolving apparatus is not shown in FIG. 2.

In FIG. 3, the reference 6 indicates the cycle of liquid mercury whichserves as a solvent. Above the liquid mercury, there is a nitrogenatmosphere which communicates by way of the passage 38 with thegasometer 56.

The boiling mercury is disposed within a boiler 50 for feeding thepassage 14 with the saturating mercury vapor for heating theinstallation. Gas heaters 51 are used for heating the mercury in theboiler 50. The numerals 52 and 53 represent containers that prevent themercury vapors in the passages 38 and 14 from mixing one with the otherand also to prevent the vapors from reaching the gasometer 56 filledwith nitrogen at the desired pressure. is the junction point of thepassages 38 and 14. A syphon 54, filled with mercury, causes thesaturating mercury vapors to flow through the passage 14 in thedirection of the arrow. The numeral 57 is a thermocouple which controlsthe heating power of the boiler for lowering when the reflux from thecondenser 53 is too great.

In FIG. 4, the reference 60 indicates an electric furnace, 61 are theresistance heaters of this furnace, 62 is the cover of the distallationvessel, 63 is the seal of this cover, 64 is an argon pipe extendingthrough the cover, 65 is a graphite plunger, 66 is the mass of liquidaluminum contained in the graphite crucible 46, and 67 is the argon gasbubbling up through the molten bath, 70 is a condenser for the mercuryvapors, 71 is the tank for receiving condensed liquid mercury, 72 is theheight ofthe barometric column filled with cold mercury when theapparatus is under vacuum, 73 is the connection with the source ofvacuum such as a vacuum pump and 74 is the argon outlet The heatinsulation arrangements have not been shown in the figure. The furnaceassembly can be made fluid-tight and can also be placed under vacuum.

According to a preferred form of the invention (FIG. 2), the impurealuminum 25 is placed in a substantially vertical column. It is held atthe bottom of this column by any means known per se, preferably by agrid 1. The liquid mercury underneath this column in a tank 4 isrecycled from the tank 4 through the pipe 3 to the column 15 by means ofa pump 3, the delivery Q of which is measured by the fiow meter 23. Inpractice, the liquid mercury is recycled several times through thiscircuit 1-4-3-23, indicated by the arrows in FIG. 2 for tricklingthrough the column of impure aluminum before being fed into the maincircuit comprising the successive stages already described in thegeneral definition of the invention, namely: the dissolution, theelimination of impurities (see FIG. 1, reference 30), and the separationof the amalgam crystals (see FIG. 1, references 40 and 47) obtained bycooling the solution thus purified.

According to another preferred form of the invention, the stream ofmercury, previously rid by any known means of the soluble impurities itmay contain, is injected into the bottom of the mass 25 of impurealuminum to be dissolved, by centripetal jets which leave orifices 2arranged at the base of the dissolving column. The height 16 of thestock of impure aluminum should be at least equal to the height 15 ofits trickling zone.

The tank 14 allows a portion q of the impure solution of aluminum inmercury to be displased by way of the overflow 5; the portion q of thissolution corresponds to the amount of fresh mercury introduced into thesystem as measured by the flow meter 24 and introduced at 8 into thedissolving column.

According to the invention, the ratio Q/q between the delivery orrecycle of the secondary trickling circuit and the portion q removed inthe overflow circuit is generally chosen to be between 3 and 50,depending upon the dis solving temperature, the state of division of theimpure aluminum and the speed of the unitary jets leaving the orifices2. Preferably, this ratio is between 10 and 25 when working in theregion of 360 C. with impure aluminum in the form of chips.

According to the invention, it is possible to vary at will the strengthof the solution of aluminum in mercury by selecting the value of thesaid ratio Q/q. A strength very close to saturation is easily obtainedby making this ratio sufiiciently large; it is also possible in anaccurate and reproducible manner to obtain a strength below that ofsaturation by reducing the said ratio.

Bearing in mind the patents and literature already referred to above, itwas unexpected that it would be possible for aluminum in the solid statewhich had not undergone any kind of pretreatment to be obtained as asolution in the mercury. It is even more surprising that such a solutionquickly reaches saturation point and as a consequence makes it possibleto achieve in a simple, economic and practically safe manner relativelylarge deliveries of a practticnlly saturated solution of aluminum inmercury without having to provide any means for regulating the rate offiow of the aluminum.

In accordance with the new process, the presence of undissolved aluminumin the solution at the outlet of the dissolving installation ispractically avoided, even with a saturated solution, whereas, in theprior processes, one:

had to be satisfied with dissolving a percentage of aluminum in asolution below saturation at corresponding temperatures.

On the other hand, in accordance with the practice of this invention,the flow of the solvent mercury is preferably effected simply by gravitybetween the dissolving apparatus and the apparatus for the eliminationof impurities, and similarly between this latter and the crystallizationapparatus, thereby to dispense with any automatic regulation of thelevels of the solvent mercury. Thus robust equipment can be used whichis subject to very little interruption and this is particularlyimportant in a process for purifying aluminum with mercury.

According to one particular form of the invention, the dissolvingtemperature is between approximately 340 and 360 C., under substantiallyatmospheric pressure.

According to one preferred form of the invention, impure aluminumcontaining 99% aluminum is purified to a refined aluminum containing99.99% aluminum.

It is advantageous, according to the invention, to make use of a pump 3immersed in the bath of liquid aluminum with a vertical shaft 3 (seeFIG. 2) as the pump for the recycling of the mercury in the column. Thepassage of the pump shaft through the Wall of the dissolving apparatusis thus in the atmosphere formed of the vapors of this apparatus and notin liquid mercury. According to one embodiment of this passage of thepump shaft through the wall, there is used a mercury hydraulic joint 17.Nevertheless, any other fluid-tight joints for this shaft can be used,such as a stuffing box with a gland or mechanical packing embedded inoil, etc.

According to one preferred form of the invention, it is possible to usea sealed chamber 9 for introducing the impure aluminum in solid forminto the dissolving apparatus. As valves for this chamber, it ispossible to use valves which are known per se formed by a sleeve ofelastically deformable rubber. The valve is closed by applying apressure (for example compressed air) to the exterior of this sleeve,which is thereby flattened. This valve ensures a hermetic sealing, evenin the presence of small pieces of aluminum between the faces of thesleeve. The application of the valves, as described above, to thepurification of aluminum with mercury thus represents a technologicaladvance in this field.

This sealed chamber is flushed with an inert gas such as nitrogen,argon, etc., as shown in FIG. 1, references 12 and 13. It is alsopossible to provide a vacuum in the said chamber. According to theinvention, by the circulation of nitrogen for flushing the air from thechamber, oxygen can be substantially completely eliminated, so that onlyless than 0.5 part per million of oxygen, for example, still remains inthe said chamber.

The present invention thus makes it possible to overcome thedifficulties previously referred to when it is desired to obtain, abovethe solution of aluminum in mercury, an atmosphere which is relativelyfree from oxygen, despite the intermittent introduction of the crudealuminum into the circuit.

According to one preferred form of the new process, the establishmentand maintenance of the temperature of the solvent mercury may be assuredby a heat-conveying fluid, such as an organic liquid, a metal or alloyin the liquid state and preferably mercury, circulating in a doublejacket of the installation to be heated. It is desirable, according tothe invention, for the mercury employed as solvent and that described asthe heating mercury to be kept under inert gas at substantially the samepressure.

It is desirable to arrange a reflux condenser on the degasifyingconduits of each circuit or cycle and thus to create, between these twocycles, a junction protected from mercury vapors by the said condensers,and connected to the said common inert gas atmosphere, as shown in FIG.3, previously referred to. The gasometer 56 can be replaced by anyapparatus ensuring a constant pressure of inert gas.

The new application to the purification of aluminum by mercury of aheatcarrying fluid, a heating method which is well known per se, hasenabled me to obtain particularly uniform temperatures at all points ofthe chamber to be heated, with the temperatures remaining relativelyconstant for any desired length of time.

It is very difficult if not impossible to obtain such a uniformity andconstancy of temperature by direct heating, particularly in chambers ofrelatively large dimensions and of complicated shapes, except byemploying an electrical heating provided with a complex control system.

The application of a heat-carrying liquid has enabled me to use asheating means the combustion of natural gases, oil, etc. These productsconstitute heat sources which are generally more ecomonical and have abetter yield of conversion into useful heat than the electricity whichis produced to a considerable part from central heating plants.

The heating by a circulation of mercury which is under substantially thesame pressure as the solvent mercury and in the state of saturatingvapor constitutes a particularly simple and efiicient means forestablishing and maintaining the temperature of the solvent mercury.

Because of the use of saturating vapor, it becomes possible to reducethe exchange surfaces and to regulate the temperatures with considerableaccuracy. On the other hand, the use of the thermocouple 57 (see theexplanations hereinbefore given in connection with FIG. 3) controls thequantity of calories consumed to that necessary for the consumption.

According to the invention, the solvent mercury can be brought to thetemperature required for the dissolution before it reaches thedissolving column by means of the heating mercury circuit.

According to the invention, the impurities which have remained insolublewhen the aluminum is dissolved in the mercury can be separated out bydecantation and skim-. ming and the solution of aluminum in the mercurysubjected to the separation of the impurities can be kept at therequired temperature by means of a heat-carrying fluid. The separationof the impurities can be effected at the same temperature as thedissolution and it is possible for maintaining the temperature at thetime of this separation to use the same heating mercury circuit as forthe dissolution.

In accordance with the invention, the impurities can be removed from thealuminum solution in mercury by means of one or more Archimedian screwswhich are slightly inclined relatively to the horizontal. Theinclination can be between 4 and 40 and preferably in the region of 10to 15. These screws preferably turn at a very low speed which inpractice is between 0.1 and 1 revolution per minute. It is advantageousfor the diameter of the impurity-separating chamber (inside which thescrew or screws turn) to have a diameter which is generally slightlylarger than that of the screw or screws, in such a way that these lattersweep over practically all the free surface of the solution in order tofree it from floating impurities.

The screw blades can be formed with grooves in their periphery tofacilitate the draining. It is possible to employ two practicallyidentical screws of opposite pitch and parallel axes which are fittedone within the other and turn in opposite directions, so that theimpurities are continuously detached from the surface of the saidscrews.

It is also possible, according to the invention, to free the solution ofaluminum in mercury from insoluble impurities by filtration, the saidfiltration preferably taking place after the decantation.

The impurities are preferably eliminated in a crucible 39 contained in asealed receiver 31 equipped for being flushed with an inert gas andwhich may also be equipped for vacuum. The valves of this sealedreceiver may, for example, be the rubber sleeve valves already describedabove. It may be expedient to use a mercury hydraulic joint as lowervalve.

According to another feature of the invention, the solution freed fromthe impurities is cooled by a fluid which is circulating in a doublejacket 47 of the crystallization apparatus. In accordance with theinvention, the said solution freed from impurities can be cooled tonormal temperature or to about or to a higher temperature. In any case,the cooling temperature is generally not higher than 160 C.

As the cooling fluid, use can be made of cold water, when it is desiredto cool to ambient temperature, boiling water for a cooling temperatureof about 100 C. and boiling chlorobenzene if it is desired to cool to132 C., boiling bromobenzene for 155 C., etc.

The specific energy consumption per kilo of purified aluminum inaccordance with the new process is small, as will be hereinafter setforth.

The saturated solution of aluminum in mercury contains 0.78% by Weightof aluminum at 400, 0.35% at 360 and 0.034% at C. and is practicallyfree from aluminum at normal temperature. An immediate calculation showsthat with a heating yield of 70% which, as already indicated above, caneasily be achieved, the heating costs (in Kcal. coming from coal, gas orfuel energy rnuch cheaper than electricity) between 360 and 20 0,substantially the equivalent of 5.3 kwh. per kg. of purified aluminum,and substantially the equivalent of 2 kwh. per kg. between 400 C. and150 C., the starting material being 99% aluminum. To these energyconsumptions for the dissolution is obviously added the energy expendedfor the purification of the amalgam by distillation, which correspondsin each case to the equivalent of about 2.5 to 3 kwh. per kg. Thesefigures show the economic interest of the new process, when they arecompared with the specific energy consumptions in the other processes:for example, 18 kwh. per kg. of 99.995% aluminum by the electrolyticprocess starting with 99.5% aluminum (the kwh. values are evaluated ashigh voltage energy). It is to be emphasized that when departing fromthe temperature range defined by the invention, the complications due totemperatures higher than 420 C. and to the corresponding pressures aresuch that the process becomes impractical.

For withdrawing the crystals of purified amalgam separated by cooling,there is used an Archimedian screw sys tem 40 (FIG. 1) which correspondsto its essential fea1 tures to that already described above forwithdrawing the impurities.

I have found that the simple treatment of draining the crystals ofpurified amalgam floating on the surface, which draining is improved bygrooves formed on the peripheries of the said Archimedian screws, issufficient to reduce the amount of merucry entrained and correspondinglyincrease the amount of aluminum in the crystals from 5% to about Thecrystals of purified amalgam are preferably collected in a crucible 46contained in a lock chamber 41. The said chamber and the said cruciblecorrespond in their essential features to those already described abovefor the recovery of the impurities.

Viewing arrangements 3'7 (FIG. 1) enable the different phases duringmanufacture to be supervised.

According to the invention, the crucible containing the impurities orthe crucible containing the purified amalgam is extracted from the lockchamber, placed in a furnace and subjected to distillation in theabsence of oxygen. There are thus recovered respectively, the mercuryentrained by the impurities or the mercury entrained by the purifiedamalgam. The distillation apparatus can be closed by a joint =63 (FIG.4).

In order to eliminate the traces of mercury retained in the aluminumafter the major part of the mercury has been recovered, it is possible,according to the invention, for this aluminum in molten state to betreated under vacuum. This latter treatment may be replaced or completed'by a flushing by means of an appropriate gas; however, I havediscovered that the most efficient treatment for the elimination of thelast traces of mercury consisting in causing a suitable gas to bubbleinto the liquid aluminum and this can, for example, be effected by thearrangement, shown in FIG. 4, or by any other bubbling arrangement. As asuitable gas for this bubbling operation, it is possible to use argon,or nitrogen, or a mixture of nitrogen and chlorine, or chlorine itself,etc.

The bubbling described above makes it possible quickly to eliminate thelast traces of mercury by means of relatively very small quantities ofunreactive gas. Because of the small quantities of this gas, it is notnecessary for it to be recycled. This simplifies the treatment for theextraction of mercury at the outlet of the apparatus. This treatment canconsist in this gas being simply washed with sprayed Water before beingreturned into the atmosphere.

This treatment for removing mercury by bubbling an appropriate gas canalso be applied to industrial aluminum alloys containing mercury, if itis desired to lower or practically cancel out the mercury contentthereof. Owing to the above treatments for ridding the aluminum of anytrace of mercury, it has been possible to regularly obtain 8 mercurycontents not exceeding 0.2 part by weight of mercury for 1 million partsof aluminum.

The following non-limitative examples are to serve to illustrate theinvention:

EXAMPLE 1 2.5 kg. per second of mercury flowing through a continuouscycle 6 (FIG. 1) are heated under atmospheric pressure from atemperature of 20 C. to a temperature of 360 C. in a heat exchanger 7,of which the heat-carrying agent flowing through a cycle 14 is thesaturating vapor of mercury under atmospheric pressure, The heatedmercury is introduced by gravity into a tank 4 containing a practicallysaturated solution of aluminum in mercury at atmospheric pressure and at360 C. (0.35%).

The mercury of the tank 4 is continuously recycled into the secondarycircuit 43-23-1 at a rate of kg. per second over aluminum chips with acontent of 99.4% by weight of aluminum.

The dissolving chamber is equipped with a double jacket, in whichcirculates the same heat-carrying fluid as in the heat exchanger. Theshaft of the pump 3 (FIG. 2) extends through the partition of thedissolving apparatus by way of a mercury hydraulic joint 17.

The solvent mercury circuit 6 and the saturated mercury vapor circuit(intended for the heating of 6) are connected to one another accordingto FIG. 3 and operate under nitrogen atmospheric pressure. From theoverflow 5, a practically saturated solution of aluminum in mer curyfiows at a rate of 2.5 kg. per second. This solution carries with it theinsoluble impurities of aluminum and a few small grains of aluminumwhich are carried through the grid 1 and which float on the surface ofsaid solution; it is poured into a decanting device which is itself alsoequipped with a double jacket directly connected to that of thedissolving chamber. The decanting device is provided with a syphonthrough which flows the saturated solution of aluminum in mercury, freedfrom its impurities. The impurities are removed by an Archimedian screw30 at an angle of 10 to the horizontal, this screw having a diameter of200 mm. and rotating at 0.2 revolution per minute in a generallycylindrical chamber which has an internal diameter of 202 mm. Theimpurities are accumulated in the crucible 39 contained in the lockchamber 31 and are periodically distilled in order to recover themercury therefrom.

The practically saturated solution flows through the overflow 36 into acrystallization apparatus provided with a water-cooled double jacket 47to cool the solution to a temperature of about 100 C. and in which thealuminum crystallizes. Two oblique screws 40 skim over the entiresurface and carry an amalgam containing 15% of aluminum and mercury intothe graphite crucible 46, where it accumulates.

Viewing devices 37 enable the various phases of the operation to besupervised. There are thus produced 200 kg. per hour of this amalgam.

The crucible is periodically removed. The lower opening of the lockchamber is formed by a mercury hydraulic joint, which enables thecrucible to be easily withdrawn. This latter is subjected todistillation in a separate furnace according to FIG. 4. When thedistillation of the mercury at atmospheric pressure in an inert gas ispractically achieved, there remain about 500 parts by Weight per millionof mercury in the aluminum. Argon is then caused to bubble at a rate of1 liter per minute through this liquid aluminum contained in thecrucible, by means of a graphite pipe, the end of which is porous. Theproduction of the furnace is 30 kg. per hour of refined aluminum with acontent of 99.993%.

EXAMPLE 2 The solvent mercury circuit 6 and the heating saturatedmercury vapor circuit 14- operate under an excess pressure of 1 kg./cm.of nitrogen with respect to atmospheric pressure (FIG. 3). The equipmentis substantially the same as that of Example 1; however, the viewingdevices 37 (FIG. 1) are omitted; the mercury hydraulic joint 17 (FIG. 2)of the pump 3 and the hydraulic joints 33 and 43 of the lock members(FIG. 1) are adapted for working under a pressure of 76 cm. of mercurysuperpressure.

The rate of flow in the solvent mercury circuit and in the secondarycircuit 3-231-5 (FIG. 2) are the same as in Example 1.

The double jacket 47 (FIG, 1) of the crystallization apparatus istraversed by bromobenzene at boiling point (temperature 155 C.). Therefined aluminum has the same content as that according to Example 1,also starting from 99.4% aluminum as starting material. However, thehourly production rate is doubled with respect to Example 1 for the samecrystallization, and the specific energy consumption per kg. of refinedaluminum produced is only approximately 40% of that according to Example1, as has already been explained above.

It will be understood that changes may be made in the details offormulation and operation without departing from the spirit of theinvention, especially as defined in the following claims.

I claim:

1. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum in a solid state with liquid mercury atelevated temperature to dissolve aluminum in the mercury, separating theformed solution of aluminum in mercury from undissolved impurities,cooling the solution of aluminum in mercury to form the solution into acrystalline phase of amalgam crystals and a liquid phase of mercury withaluminum dissolved therein separating the amalgam crystals from theremainder and then removing mercury by vaporization from the amalgamcrystals to leave purified aluminum, and a secondary cycle comprisingthe step which includes the portion of the main stream of flowing liquidmercury into contact with the solid particles of impure aluminum todissolve out aluminum, and which includes the step of draining theliquid mercury with aluminum dissolved therein from the impure aluminum,recycling the drained liquid mercury for flowing into contact with thesolid particles of impure aluminum and repeating the secondary cycle fora number of times, continuously bleeding a fraction of the drainage ofthe liquid mercury with the aluminum dissolved therein to the mainstream for separation of undissolved impurities and for separation ofdissolved aluminum, and adding liquid mercury to the secondary cycle inan amount corresponding to the amount removed from the secondary cycleinto the main stream in which the main stream and secondary cycle arecarried out as a continuous operation.

2. The process as claimed in claim 1 in which the liquid mercury isintroduced into the column of impure aluminum by jet streams for flowinto contact with the impure aluminum.

3. The process as claimed in claim l which includes the step ofmaintaining the solution zone under inert atmosphere.

4. The process as claimed in claim 1 in which the impure aluminumcontains at least 99% by weight of aluminum.

5. The process as claimed in claim 1 which includes the step ofintroducing impure aluminum into the solution zone from a sealed feedzone in communication with the solution zone.

6. The process as claimed in claim 1 wherein the portion bled from thesecondary cycle into the main stream is caused to flow gravitationallyfrom the main stream to the separation zone for the separation ofundissolved impurities and to the cooling zone for crystallization ofamalgam.

7. The process as claimed in claim 1 in which undissolved impuritiesfloat on the surface of the liquid mercury having aluminum dissolvedtherein and which includes the step of separating the undissolvedimpurities by skimming the impurities from the top of the liquid.

3. The process as claimed in claim 7 in which the undissolved impuritiesare removed from the dissolving liquid by a separating screw operatingwithin a housing at an angle of 4 to 40.

9. The process as claimed in claim 1 in which the portion bled from thesecondary cycle into the main stream is caused to flow gravitationallyfrom the main stream to the separation zone for the separation ofundissolved impurities and in which theundissolved impurities float tothe surface of the liquid mercury having aluminum dissolved therein andwhich includes the step of separating the undissolved impurities fromthe solution of aluminum in mercury by filtration.

10. The process as claimed in claim 1 in which the crystals of amalgamare separated from the remainder of the liquid by a screw separatoroperating within a housing at an angle of 4 to 40.

11. The process as claimed in claim 1 which includes collecting theseparated crystallized amalgam in a receiver, distilling the mercuryfrom the amalgam to leave substantially a purified aluminum andmaintaining an inert atmosphere during the collecting and distillingsteps.

12. The process as claimed in claim 11 which includes the step ofremoving the last traces of mercury from the purified aluminum by avacuum distillation.

'13. The process as claimed in claim 11 in which the space above thepurified aluminum is flushed with an inert gas for removal of traces ofmercury.

14. The process as claimed in claim 1 in which an inert gas is bubbledthrough the purified aluminum for removal of traces of mercury and formaintaining the inert atmosphere above the aluminum.

15. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solu tion zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowingliquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thecycle a number of times, continuously bleeding a fraction of thedrainage of the liquid mercury with aluminum dissolved therein to themain stream for separation of undissolved impurities and for separationof dissolved aluminum, and adding liquid mercury to the secondary cycle.in an amount corresponding to the amount removed from the secondarycycle into the main stream, in which l/3 to 1/50 of the mercury streamin the secondary cycle is continuously bled into the main stream forsubsequent treatment to separate impurities and purified aluminum. i

16. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain ll undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thecycle a number of times, continuously bleeding a fraction of thedrainage of the liquid mercury with aluminum dissolved therein to themain stream for separation of undissolved impurities and for separationof dissolved aluminum, and adding liquid mercury to the secondary cyclein an amount corresponding to the amount removed from the secondarycycle into the main stream, in which 1/10 to 1/25 of the mercury streamof the secondary cycle is continuously bled into the main stream forsubsequent treatment to separate impurities and purified aluminum.

17. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreat ment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thecycle a number of times, continuously bleeding a fraction of thedrainage of the liquid mercury with aluminum dissolved therein to themain stream for separation of undissolved impurities and for separationof dissolved aluminum, and adding liquid mercury to the secondary cyclein an amount corresponding to the amount removed from the secondarycycle into the main stream, which includes the step of heating themercury in the secondary cycle to a temperature within the range of 340to 360 C. before being brought into contact with the solid impurealuminum and maintaining the pressure at about atmospheric duringsolution.

18. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals. separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum,

and a secondary cycle comprising the steps which include the portion ofthe main stream of flowing liquid mercury into contact with the solidparticles of impure aluminum to dissolve out aluminum and which includesthe steps of draining the liquid mercury with aluminum dissolved thereinfrom the impure aluminum, recycling the drained liquid mercury forflowing into contact with the solid particles of impure aluminum andrepeating the cycle a number of times, continuously bleeding a fractionof the drainage of the liquid mercury with aluminum dissolved therein tothe main stream for separation of undissolved impurities and forseparation of dissolved aluminum, and adding liquid mercury to thesecondary cycle in an amount corresponding to the amount removed fromthe secondary cycie into the main stream, in which the liquid mercury inthe secondary cycle is drained from the impure aluminum into a storagezone and wherein the liquid mercury is recycled from the storage zone tothe column of impure aluminum by a means which is completely submergedin the liquid mercury in the storage zone.

1'9. The process as claimed in claim 13 in which the secondary cycleincluding the solution zone is maintained within a sealed enclosure andin which the displacement means is operated through a shaft extendingoutwardly of the sealed enclosure to a driving means located outside ofthe sealed enclosure.

20. The process as claimed in claim 19 which includes circulating aninert gas through the sealed enclosure for removal of oxygen and formaintaining a non-oxidizing atmosphere therein.

21. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thecycle a number of times, continuously bleeding a fraction of thedrainage of the liquid mercury with aluminum dissolved therein to themain stream for separation of undissolved impurities and for separationof dissolved aluminum, and adding liquid mercury to the secondary cyclein an amount corresponding to the amount removed from the secondarycycle into the main stream, in which a heat transfer fluid is circulatedin heat exchange relationship with the dissolving mercury in thesecondary cycle and the solution zone to maintain the desiredtemperature of solution.

22. The process as claimed in claim 21 in which the heat transfer liquidis mercury in the form of a saturated vapor.

23. The process as claimed in claim 21 in which the solvent mercury andthe heat transfer fluid are maintained under uniform pressure of aninert gas.

24. The process as claimed in claim 21 in which the heat transfer liquidis mercury and in which the mercury heat transfer fluid and the solventmercury have a common communication zone communicating with an inert gasand wherein the mercury vapors are blocked from passage from secondarycycle to the main stream by condensation.

25. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained mercury for flowing into contactwith the solid particles of impure aluminum and repeating the cycle anumber of times, continuously bleeding a fraction of the drainage of theliquid mercury with aluminum dissolved therein to the main stream forseparation of undissolved impurities and for separation of dissolvedaluminum, and adding liquid mercury to the secondary cycle in an amountcorresponding to the amount removed from the secondary cycle into themain stream, in which the treatment with mercury to dissolve aluminumfrom the impure aluminum and the separation of impurities from thesolution of aluminum dissolved in mercury are carried out atsubstantially the same temperatures.

26. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum with liquid mercury at elevatedtemperature to dissolve aluminum in the mercury, separating the formedsolution of aluminum in mercury from undissolved impurities, cooling thesolution of aluminum in mercury to form amalgam crystals, separating theamalgam crystals from the remainder of liquid mercury having aluminumdissolved therein, and then removing mercury by vaporization from theamalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles of impurealuminum to dissolve out aluminum and which includes the steps ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling the drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thecycle a number of times, continuously bleeding a fraction of thedrainage of the liquid mercury with aluminum dissolved therein to themain stream for separation of undissolved impurities and for separationof dissolved aluminum, and adding liquid mercury to the secondary cyclein an amount corresponding to the amount removed from the secondarycycle into the main stream, which includes the step of cooling thesolution of aluminum in mercury in the main stream, after separation ofundissolved impurities, to a temperature below 160 C. to crystalizeamalgam.

27. In the process of purification of aluminum by treatment of impurealuminum with mercury in a solution zone to dissolve out aluminum whileimpurities remain undissolved including a main stream comprising thetreatment of the impure aluminum in a solid state with liquid mercury atan elevated. temperature within the range of 300420 C. to dissolvealuminum in the mercury, separating undissolved impurities from thesolution of aluminum in mercury, cooling the separated solution ofaluminum in mercury to form amalgam crystals, separating the amalgamcrystals from the remainder and then removing mercury by vaporization ofthe amalgam crystals to leave purified aluminum, and a secondary cyclecomprising the steps which include the portion of the main stream offlowing liquid mercury into contact with the solid particles: of impurealuminum to dissolve out aluminum, and which includes the step ofdraining the liquid mercury with aluminum dissolved therein from theimpure aluminum, recycling drained liquid mercury for flowing intocontact with the solid particles of impure aluminum and repeating thesecondary cycle, continuously bleeding a fraction of the drainage of theliquid mercury with aluminum dissolved therein to the main stream forseparation of undissolved impurities and for separation of dissolvedaluminum, and adding liquid mercury to the secondary cycle in an amountcorresponding to the amount bled from the secondary cycle into the mainstream.

References Cited UNITED STATES PATENTS 1,961,135 6/1934 Grahon et al. 81X 1,200,832 10/1916 Greenway 23272.6 X 2,042,661 6/1936 Jeremiassen23-273 2,055,836 9/1936 Cowles 23-272.6 X 2,154,465 4/1939 Mills et al.266-12 2,279,580 4/ 1942 Miner 266-42 2,331,988 10/1943 Loevenstein.

2,784,080 3/ 1957 Schmidt 7563 2,795,498 6/ 1957 Messner 75-68 3,102,8059/1963 Messner 75-68 3,116,998 1/1964 P'agonis 75-68 X 3,129,066 4/1964Ambrogi et al. 23-272.6 X

DAVID L. RECK, Primary Examiner. HYLAND BIZOT, Examiner.

H. W. TARRING, Assistant Examiner.

1. IN THE PROCESS OF PURIFACTION OF ALUMINUM BY TREATMENT OF IMPURE ALUMINUM WITH MERCURY IN A SOLUTION ZONE TO DISSOLVE OUT ALUMINUM WHILE IMPURITIES REMAIN UNDISSOLVED INCLUDING A MAIN STREAM COMPRISING THE TREATMENT OF THE IMPURE ALUMINUM IN A SOLID STATE WITH LIQUID MERCURY AT ELEVATED TEMPERATUE TO DISSOLVE ALUMINUM IN THE MERCURY, SEPARATING THE FORMED SOLUTION OF ALUMINUM IN MERCURY FROM UNDISSOLVED IMPURITIES COOLING THE SOLUTION OF ALUMINUM IN MERCURY TO FORM THE SOLUTION INTO A CRYSTALLINE PHASE OF AMALGAM CRYSTALS AND A LIQUID PHASE OF MERCURY WITH ALUMINUM DISSOLVED THEREIN SEPARATING THE AMALGAM CRYSTALS FROM THE REMAINDER AND THEN REMOVING MERCURY BY VAPORIZATION FROM THE AMALGAM CRYSTALS TO LEAVE PURIFIED ALUMINUM, AND A SECNDARY CYCLE COMPRISING THE STEP WHICH INCLUDES THE PORTION OF THE MAIN STREAM OF FLOWING LIQUID MERCURY INTO CONTACT WITH THE SOLID PARTICLES OF IMPURE ALUMINUM TO DISSOLVE OUT ALUMINUM, AND WHICH INCLUDES THE STEP OF DRAINING THE LIQUID MERCURY WITH ALUMINUM DISSOLVED THEREIN FROM THE IMPURE ALUMINUM, RECYCLING THE DRAINED LIQUID MERCURY FOR FLOWING INTO CONTACT WITH THE SOLID PARTICLES OF IMPURE ALUMINUM AND REPEATING THE SECONDARY CYCLE FOR A NUMBER OF TIMES, CONTINUOUSLY BLEEDING A FRACTION OF THE DRAINAGE OF THE LIQUID MERCURY WITH THE ALUMINUM DISSOLVED THEREIN TO THE MAIN STREAM FOR SEPARATION OF UNDISSOLVED IMPURITIES AND FOR SEPARATION OF DISSOLVED ALUMINUM, AND ADDING LIQUID MERCURY TO THE SECONDARY CYCLE IN AN AMOUNT CORRESPONDING TO THE AMOUNT REMOVED FROM THE SECONDARY CYCLE INTO THE MAIN STREAM IN WHICH THE MAIN STREAM AND SECONDARY CYCLE ARE CARRIED OUT AS A CONTINUOUS OPERATION. 